Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel injection, or delivery, uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel injection uses a direct injector for each cylinder. One of the considerations when choosing an appropriate fuel delivery system may be the fuel type present in the fuel tank. With the recent advent of alternate fuels such as alcohol-based fuels and fuel blends for automotive applications, various engine control systems may make adjustments to a variety of engine operations, for example fuel injection timing, spark timing, or boost, based on the alcohol content of the engine fuel.
One such example is described in U.S. Pat. No. 7,287,509 wherein an alcohol-fuelled engine is described that utilizes direct injection along with an appropriate alcohol content based boost, spark timing, and fuel control system to permit efficient performance. The engine's control system also adjusts valve operation based on the alcohol content of the fuel.
However, the inventors have herein recognized a potential issue with such an approach. Specifically, valve timing settings that ignore various interactions between fuel type and injection type may lead to degraded performance. For example, operating constraints related to engine knock, combustion stability, and an available intake manifold pressure, can each be affected not only by fuel type and injection type, but also by the interactions among fuel types and injection types.
In one example, the above issues may be addressed by a method of operating an engine in a vehicle having variable valve operation for an intake and/or exhaust valve of the cylinder, the method comprising: delivering a first fuel to a cylinder of the engine from a first injector; delivering a second fuel to the cylinder of the engine from a second injector, where a composition of at least one of the first or second fuels varies; and adjusting the variable valve operation responsive to the varying composition and further based on variation in the delivery of the first or second fuel.
By adjusting valve operation, such as valve timing, based on a fuel composition, and the delivery of a first and second fuel, it may be possible to take into account interactions between them. For example, valve timing may be adjusted responsive to variation in the amount of ethanol in a fuel blend that is directly injected into the engine, as well as responsive to the relative distribution of the total amount of injected fuel from among a plurality of injectors for the cylinder. Such compensation may allow the engine to operate efficiently even when the fuel type and injection type changes dynamically during engine operation.
In one particular example, the engine may shift delivery of fuel to a cylinder from predominately direct injection to predominately port injection (e.g., due to a decrease in engine load). In a first circumstance, the directly injected fuel may have a higher ethanol amount (e.g., E85), whereas in a second circumstance it may have a lower ethanol amount (e.g., E50), depending on what fuels an operator adds. However, in the first circumstance, the valve timing may be advanced/retarded to a greater/lesser extent than that of the second circumstance to reduce issues related to combustion stability, for example. In this way, improved operation may be achieved taking into consideration interactions between the fuel composition variation and the location from where the fuel is delivered to the cylinder.
Note that various valve operation adjustments may be used, such as advancing valve timing, retarding valve timing, increasing valve lift, decreasing valve lift, increasing valve overlap, decreasing valve overlap, advancing intake valve opening, retarding intake valve opening, advancing intake valve closing, retarding intake valve closing, advancing exhaust valve opening, retarding exhaust valve opening, advancing exhaust valve closing, retarding exhaust valve closing, and combinations thereof, for example.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.